Unfortunatly England has a law that makes it a serious crime to keep this sort of thing. Even without deed restrictions, anyone finding ancient artifacts on their property in England has to turn it over to the state...their laws assume that these artifacts belong to society, not the landowner. While I can see both sides of this issue, it would REALLY suck to find a bag of old Roman gold coins and have to turn them over to the local museum.
BTW, I agree about the thrill of holding ancient artifacts. I collect old coins and artifacts, and the oldest pieces in my collection are ~5000 years old (a couple of Sumerian jewelry pieces). Just thinking about the history they've seen and the huge number of people who have owned them before me is incredibly cool, and really helps to make history more "real".
There is legisalation in the UK that compensates finders. I've not read about anyone complaining about their compensation.